CN112019295B - Orthogonal mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation - Google Patents

Abstract

The invention discloses an orthogonal mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation, which belongs to the technical field of optical transmission.A series-parallel conversion unit is used for carrying out series-parallel conversion on input original data and then completing coding mapping in an APPM mapping unit, an up-sampling unit is used for carrying out orthogonal filtering on coded signals, and an adder unit is used for adding the filtered signals to synthesize a path of three-dimensional APPM signals for orthogonal mode transmission; the method realizes multiplexing of three paths of pulse amplitude modulation (APPM) signals based on three groups of orthogonal filters, further realizes great multiplication of transmission capacity by combining an orthogonal mode multiplexing transmission method, improves the problem of low APPM frequency spectrum efficiency, increases the transmission capacity, and provides a possibility for APPM to be expanded to more dimensions; meanwhile, the transmission scheme of orthogonal mode multiplexing eliminates mode crosstalk in few-mode optical fibers, MIMO-DSP processing is not needed at a receiving end, system cost is reduced, and high-capacity transmission with low complexity is realized.

Description

Orthogonal Mode Multiplexing Transmission Method Based on 3D Pulse Amplitude Position Modulation

technical field

The invention belongs to the technical field of optical communication, and in particular relates to an orthogonal mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation.

Background technique

With the acceleration of informatization construction, network users have surged, and network traffic has shown explosive growth. According to the report, from 2017 to 2022, mobile data traffic will grow at a compound annual growth rate (CAGR) of 46%, and by 2022 Year will reach 77.5 exabytes per month. In order to solve this problem, mode multiplexing technology based on few-mode fiber is an indispensable technical solution, because it uses different modes in the few-mode fiber as different spatial channels for data transmission, thereby increasing the transmission capacity exponentially. In the mode multiplexing system, although all orthogonal spatial modes and polarization modes in few-mode fiber (FMF) are used as independent data channels, in actual fiber transmission, the various modes in FMF will be The various influencing factors in the link are coupled, resulting in crosstalk, which affects the quality of transmitted information. In response to this problem, some researchers use multiple-input multiple-output (MIMO) DSP processing solutions, and these MIMO algorithms can effectively solve the problem of mode crosstalk, but there are problems of high cost and high complexity of MIMO, which is more suitable for long-distance transmission and It is not short-distance optical transmission, so it becomes necessary to find a low-complexity and high-efficiency multiplexing method suitable for short-distance transmission.

At the same time, in the short-distance optical communication system, in order to accommodate more users and meet the needs of transmission capacity, the development of short-distance transmission has changed from the classic non-return-to-zero time division multiplexing (NRZ-TDM) to wavelength division multiplexing (WDM). and more advanced modulation formats. For example, Orthogonal Frequency Division Multiplexing (OFDM), Carrier-Free Amplitude-Phase (CAP) modulation, Discrete Multitone Modulation (DMT), Pulse Amplitude Modulation (PAM), etc., these modulation formats can keep the bandwidth and number of channels unchanged. to obtain higher transmission capacity. Among these advanced modulation formats, the peak-to-average power of PAM-4 is significantly lower than that of DMT modulation technology, and the receiver sensitivity is better than that of CAP16 under the same bit rate, so it has attracted the interest of many researchers. However, the power loss of PAM increases exponentially with the increase of modulation order, and high-order PAM is prone to the problem of symbol crosstalk, which increases the difficulty of receiving decision. Pulse position modulation (PPM) divides the symbol into multiple sub-intervals, and there is only one pulse signal in each interval, which has the advantages of higher power efficiency and stronger resistance to intersymbol interference, but it also has low bandwidth utilization. Shortcomings. Pulse Amplitude Position Modulation (APPM) achieves a trade-off between power consumption and bandwidth utilization by utilizing both pulse amplitude and position to convey information, and can be viewed as a hybrid combination of M-PPM and M-PAM modulation formats. However, the traditional APPM also has the problems of large bandwidth occupation and low spectral efficiency. Its use in high-speed transmission systems is limited, and a new modulation method combining pulse amplitude and position is required.

Since there is only one pulse with information in each symbol period of the APPM signal, it is easy to cause the problem of large bandwidth occupation and low spectral efficiency. At the same time, the traditional APPM only has a single dimension, and it is difficult to improve the transmission capacity and cannot meet the large bandwidth demand. Large-scale, high-flexibility short-distance transmission requirements; at the same time, the mode crosstalk problem that inevitably occurs in traditional mode multiplexing systems, there is no targeted method to optimize and compensate for the two at the same time.

SUMMARY OF THE INVENTION

Purpose of the invention: In order to improve the problem of mode crosstalk in the traditional few-mode transmission system and the problem of low spectral efficiency in the traditional APPM modulation, the purpose of the present invention is to provide an orthogonal mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation, based on large capacity. , low complexity, high spectral efficiency transmission demands and mode crosstalk generation mechanism, using the orthogonal mode multiplexing system based on three-dimensional pulse amplitude position modulation for transmission.

Technical scheme: in order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme:

The orthogonal mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation, the input original data is subjected to serial-to-parallel conversion by the serial-to-parallel conversion unit, and then the coding and mapping are completed in the APPM mapping unit. The encoded signal passes through the up-sampling unit and then passes through the filter. The unit performs quadrature filtering, and the signals after quadrature filtering are added by the adder unit to synthesize a three-dimensional APPM signal and then transmit in quadrature mode.

Further, include the following steps:

1) The serial-parallel conversion unit converts the input original data into parallel transmission data;

2) The data transmitted in parallel in the step 1) obtains the signal mapped by the APPM through the APPM mapping unit, and then performs encoding and transmission;

The signal mapped by APPM has a pulse in one time slot in each symbol period, and the other time slots are 0. There are eight different combinations of such pulses;

3) Up-sampling the APPM-mapped signal described in step 2) by the up-sampling unit to realize the periodic extension of the signal on the spectrum, and obtain three APPM signals; in the up-sampling unit, perform a certain multiple of Sampling can recover the transmitted information at the receiving end, while reducing the number of taps required by the filter;

4) Filter the signal obtained in step 3) by the filter unit; multiply the APPM signal after the upsampling unit by three mutually orthogonal filters to maintain the orthogonality of the three APPM signals;

5) Synthesize the three APPM signals in step 4) into one through the adder unit to obtain a complete three-dimensional APPM signal, which is then transmitted in the orthogonal mode multiplexing system.

Further, in step 1), the input original data is divided into three data streams after serial-parallel transformation, and multi-dimensional multiplexing is performed.

Further, in step 2), each of the three data streams generated by the serial-to-parallel change is subjected to 2×4APPM mapping through the APPM mapping unit.

Further, in the 2×4 APPM, each symbol has three bits, one bit is used for amplitude matching, and two bits are used for position matching; wherein, i represents the amplitude bit, and {0}, {1} correspond to is v ₁ , v ₂ with two different amplitudes, and the probability of two pulses of different amplitudes appearing is equal, which is 1/2; j represents the position bit, and the combination of { y ₁ , y ₂ } is used to select from four time slots One is to filter the energy signal, and complete the process of pulse amplitude position modulation through the selection and combination of i and j . The generated APPM signal has only one time slot pulse in each symbol period, and the pulse amplitude of other time slots is 0. Such pulses have a total of There are eight different combinations.

Further, in step 4), the filtering of the signal obtained in step 3) is to use the minimax optimization algorithm to obtain three mutually orthogonal filter units, and the frequency response curve of the orthogonal filter is expressed by the formula. for:

Among them, f _i is the impulse response of the i -th filter at the sending end, f ₁ is the impulse response of the first filter at the sending end, f ₂ is the impulse response of the second filter at the sending end, and f ₃ is the first filter at the sending end Three-way filter impulse response, F is the frequency amplitude characteristic of f _i , F ₁ is the frequency amplitude characteristic of the filter f ₁ , F ₂ is the frequency amplitude characteristic of the filter f ₂ , F ₃ is the frequency amplitude characteristic of the filter f ₃ frequency-amplitude characteristics; H is the target bandpass frequency response; R(Z) is the polyphase decomposition of the receiver filter bank in the linear constraint, S(Z) is the polyphase decomposition of the transmitter filter bank, Γ is the permutation matrix, I is a unit matrix, Z ^-n represents n delay elements, and the matched filter of the receiver response is calculated through this linear constraint; on the basis of the PR condition, using the optimization principle, such that I F ₁ -H I, I F ₂ -H1 , 1F ₃ -H1 The largest of the three terms tends to be the smallest, and finally through iterative optimization _, the part of the transmit filter Fi that exceeds the target bandpass frequency response tends to be the smallest.

Further, in step 5), the combination of the three channels of APPM signals in step 4) by the adder unit is specifically: at the transmitting end, according to the principle of the orthogonalized mode field that the mode field correlation coefficient is 0, the laser The continuous light generated by the source realizes the regulation of the mode field after passing through the SLM, and outputs orthogonal mode light with different mode spot radii, providing light input for the MZM to realize intensity modulation; the three-dimensional APPM on the electrical domain converts the digital signal through a digital-to-analog converter. into an analog signal waveform, which is then used to drive the MZM; the light of each mode loaded with the three-dimensional APPM is optically amplified by an erbium-doped fiber amplifier (EDFA) and then synthesized through an orthogonal photonic coupler.

At this time, the mode spot radius of each mode presents a step-like increasing radius ( a ₁ < a ₂ <... < a _N ), and the superposition appears as the arrangement of concentric circles with different radii. The information-carrying orthogonal mode light coupled into one channel is transmitted in a 25KM few-mode fiber.

Contrary to the working process of the transmitting end, at the receiving end, the optical signal of the receiving end first passes through an optical filter, which can filter out the amplifier spontaneous emission noise (ASE) noise generated by the EDFA in the transmitting end, and at the same time can filter out the channel Noise; then through an adjustable optical attenuator (VOA) to adjust the received optical power, the photodetector is used to detect the received optical signal and convert it into an electrical signal, and finally perform three-dimensional APPM demodulation and bit error rate calculation on the computer side.

The quadrature mode multiplexing method based on three-dimensional pulse amplitude position modulation can be embodied in two aspects: first, the input original data is divided into three parts after serial-parallel transformation, and each is mapped to form a three-way 2 ×4APPM matching signal, then the three-way signals are up-sampling and three sets of mutually orthogonal filters to generate mutually orthogonal three-dimensional signals, and then after an adder, the three-way signals are combined into one, and a Three-dimensional APPM signal; secondly, the continuous light output by the laser source is controlled by the spatial light modulator (SLM) to output multiple orthogonal mode lights with different mode spot radii. The cross-correlation coefficient is 0, and the modes are orthogonal to each other. After the generated multiple orthogonal mode lights are respectively loaded with three-dimensional APPM signals, they are synthesized by an orthogonal photonic coupler and transmitted in a few-mode fiber.

Beneficial effect: Compared with the prior art, the orthogonal mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation of the present invention, aiming at the advantages of low spectral efficiency of APPM but high transmission quality, by reducing the sampling multiple requirement in the sampling process , and the required number of filter taps, reducing the complexity and cost of the system. At the same time, the three-dimensional APPM multiplexing based on three sets of orthogonal filters effectively improves the system transmission capacity and provides the possibility for the system to expand to a higher dimension; The orthogonal mode multiplexing transmission method reduces the mode crosstalk by eliminating the overlap between the modes, which can realize multi-mode multiplexing transmission without MIMO processing at the receiving end, reduce the system complexity and cost, and effectively improve the transmission system capacity.

Description of drawings

1 is a flowchart of an orthogonal mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation;

Figure 2 is a schematic diagram of three-dimensional pulse amplitude position modulation;

Figure 3 is the 2×4APPM mapping rule;

Fig. 4 is the three-dimensional filter frequency response that is orthogonal to each other;

Fig. 5 is the transmission experiment scheme of the present invention;

Fig. 6 is the simulation result of the bit error rate of the present invention.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments.

An orthogonal mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation. After the up-sampling unit, the filter unit is used for orthogonal filtering, and the orthogonally filtered signal is added by the adder unit to synthesize a three-dimensional APPM signal for transmission in the orthogonal mode. Specifically include the following steps:

1) Serial-parallel conversion unit

The serial-to-parallel conversion unit converts the input data into data for parallel transmission; in order to perform multi-dimensional multiplexing, the input original data is divided into three data streams after serial-to-parallel conversion;

2) APPM mapping unit

For better coded transmission, the three data streams in step 1) need to be mapped by APPM; only one time slot has a pulse in each symbol period of the signal mapped by APPM, and the other time slots are 0. There are eight such pulses in total. different combinations;

3) Upsampling unit

In order to realize the periodic extension of the signal in the frequency spectrum, it is necessary to upsample the APPM mapped signal in step 2). number of taps required;

4) Filter unit

In order to maintain the orthogonality of the three APPM signals, the signals obtained in step 3) are filtered; we multiply the APPM signals after the upsampling unit by three mutually orthogonal filters;

5) Adder unit

In order to obtain a complete three-dimensional APPM signal, the three-way signals in step 4) are combined into one through the adder unit, and then transmitted in the orthogonal mode multiplexing system.

In step 2), each of the three data streams generated by the serial-to-parallel change undergoes 2×4 APPM mapping through the APPM mapping unit. In 2x4APPM, each symbol has three bits, one bit for amplitude matching and two bits for position matching. In the figure i represents the amplitude bit, {0}, {1} correspond to two different amplitudes v ₁ , v ₂ , the probability of the two pulses with different amplitudes appearing is equal, which is 1/2; j represents the position bit, { The combination of y ₁ , y ₂ } is used to select one of the four time slots for energy signal filtering, and the process of pulse amplitude position modulation is completed through the selection and combination of i and j , and the generated APPM signal has only one time slot in each symbol period. There are pulses in the slot, and the pulse amplitude in other time slots is 0. There are eight different combinations of such pulses.

In step 3), the above sampling multiple is 4 as an example, and the frequency spectrum period is extended by 4 times. The sampling method is as follows: Assume that the input first 2×4APPM signal is {0,2,0,0,1,…}, after 4 times of upsampling, it becomes {0,0,0,0,2,0, 0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,…}.

In step 4), in order to maintain the orthogonality of the three APPM signals, the signals obtained in step 3) are filtered. Use the minimax optimization algorithm to obtain three mutually orthogonal filter units (including filter unit 1, filter unit 2, filter unit 3), and the frequency response curve of the orthogonal filter can be expressed by the formula. for:

Among them, f _i is the impulse response of the i -th filter at the sending end, f ₁ is the impulse response of the first filter at the sending end, and similarly, f ₂ and f ₃ are the second and third filter impulse responses. response. F is the frequency amplitude characteristic of f _i , that is, F ₁ is the frequency amplitude characteristic of the filter f ₁ , F ₂ is the frequency amplitude characteristic of the filter f ₂ , and F ₃ is the frequency amplitude characteristic of the filter f ₃ . H is the target bandpass frequency response; R(Z) , S(Z) are the polyphase decomposition of the receiver and transmitter filter banks in the linear constraint, Γ is the permutation matrix, I is the identity matrix, and Z - ⁿ represents n Delay element, the matched filter of the receiver response is calculated by this linear constraint. According to the above equations, on the basis of PR conditions, using the optimization principle, the largest one of the three items of 1F ₁ -H1 , 1F ₂ -H1 , and 1F ₃ -H1 tends to be the smallest, and finally passes The iterative optimization minimizes the portion of the transmit filter Fi that exceeds the target _bandpass frequency response.

In step 5), the system scheme of the orthogonal mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation is shown in FIG. 5 . At the sending end, according to the principle of orthogonalized mode field with the mode field correlation coefficient being 0, the continuous light generated by the laser source is controlled by the mode field after passing through the SLM, and the orthogonal mode light with different mode spot radii is output to provide optical input for the MZM , to achieve intensity modulation. The three-dimensional APPM on the electrical domain converts the digital signal into an analog signal waveform via a digital-to-analog converter, which is then used to drive the MZM. The light of each mode loaded with the three-dimensional APPM is optically amplified by an erbium-doped fiber amplifier (EDFA) and then synthesized into one channel by an orthogonal photonic coupler. At this time, the mode spot radius of each mode presents a step-like increasing radius ( a ₁ < a ₂ <... < a _N ), and the superposition appears as the arrangement of concentric circles with different radii. The information-carrying orthogonal mode light coupled into one channel is transmitted in a 25KM few-mode fiber.

At the receiving end, contrary to the working process of the transmitting end, the optical signal at the receiving end first passes through an optical filter, which can filter out the amplifier spontaneous emission noise (ASE) noise generated by the EDFA in the transmitting end, as well as the channel noise. Then, the received optical power is adjusted through an adjustable optical attenuator (VOA), and the photodetector is used to detect the received optical signal and convert it into an electrical signal. Finally, the three-dimensional APPM demodulation and bit error rate calculation are performed on the computer.

Example

Figure 1 shows the system flow chart of the present invention. The original data is subjected to three-dimensional APPM mapping to realize multi-dimensional multiplexing of 3-channel APPM signals. At the same time, N laser sources obtain multiple orthogonal modes with different mode spot radii after SLM. The light is then multiplexed in quadrature mode by the three-dimensional APPM signal passing through a digital-to-analog converter (ADC) under the action of a Mach-Zehnder modulator (MZM). The three-dimensional pulse amplitude position modulation is the core content of the present invention. As shown in Figure 2, the process can be divided into serial-parallel conversion, APPM mapping, upsampling, filter and adder. The specific workflow of each module is as follows:

(1) Serial-parallel conversion unit

For multi-dimensional multiplexing, the input raw data is divided into three data streams after serial-parallel transformation.

(2) APPM mapping unit

In this way, in each symbol period of the APPM-mapped signal, only one time slot has a pulse and the other time slots are 0. There are eight different combinations of such pulses.

Each of the three data streams generated by the serial-parallel change is mapped to 2×4 APPM, and the mapping rules are shown in Figure 3. In 2x4APPM, each symbol has three bits, one bit for amplitude matching and two bits for position matching. In the figure i represents the amplitude bit, {0}, {1} correspond to two different amplitudes v ₁ , v ₂ , the probability of the two pulses with different amplitudes appearing is equal, which is 1/2; j represents the position bit, { The combination of y ₁ , y ₂ } is used to select one of the four time slots for energy signal filtering, and the process of pulse amplitude position modulation is completed through the selection and combination of i and j , and the generated APPM signal has only one time slot in each symbol period. There are pulses in the slot and other time slots are 0. There are eight different combinations of such pulses.

(3) Upsampling unit

In the up-sampling unit, performing up-sampling by a certain multiple can restore the transmitted information at the receiving end, and at the same time reduce the requirement for the number of taps of the filter. In a system with a sampling multiple of 4, the sampling method is as follows: Assuming that the first 2×4 APPM signal is {0,2,0,0,1,…}, it becomes {0,0 after 4 times of upsampling ,0,0,2,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,…}.

(4) Filter unit

In order to perform three-dimensional multiplexing of APPM, we multiply the upsampled APPM signal by three mutually orthogonal filters. The present invention uses the minimax optimization algorithm to obtain three mutually orthogonal filter units, and FIG. 4 is the frequency response curve diagram of the orthogonal filter adopted in the present invention, which can be specifically expressed as:

Among them, f _i is the impulse response of the i -th filter at the sending end, f ₁ is the impulse response of the first filter at the sending end, and similarly, f ₂ and f ₃ are the second and third filter impulse responses. response. F is the frequency amplitude characteristic of f _i , that is, F ₁ is the frequency amplitude characteristic of the filter f ₁ , F ₂ and F ₃ are the frequency amplitude characteristics of the filter f ₂ and f ₃ , and H is the target band-pass frequency response; linear constraint where R (Z) , S(Z) are the polyphase decomposition of the receiver and transmitter filter banks, Γ is the permutation matrix, I is the identity matrix, and Z - ⁿ represents n delay elements. matched filter with end-response. According to the above equations, on the basis of PR conditions, the optimization principle is used to make the largest one of the three items of 1F ₁ -H1 , 1F ₂ -H1 and 1F ₃ -H1 tend to be the smallest, and finally pass the The iterative optimization minimizes the portion of the transmit filter Fi that exceeds the target _bandpass frequency response.

(5) Adder unit

The three-way orthogonal signals after orthogonal filtering are synthesized by a simple addition operation through the adder unit.

The system scheme of the orthogonal mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation is shown in Fig. 5 . At the sending end, according to the principle of orthogonalized mode field with the mode field correlation coefficient being 0, the continuous light generated by the laser source is controlled by the mode field after passing through the SLM, and the orthogonal mode light with different mode spot radii is output to provide optical input for the MZM , to achieve intensity modulation. The three-dimensional APPM on the electrical domain converts the digital signal into an analog signal waveform via a digital-to-analog converter, which is then used to drive the MZM. The light of each mode loaded with the three-dimensional APPM is optically amplified by an erbium-doped fiber amplifier (EDFA) and then synthesized into one channel by an orthogonal photonic coupler. At this time, the mode spot radius of each mode presents a step-like increasing radius ( a ₁ < a ₂ <... < a _N ), and the superposition is shown as the arrangement of concentric circles with different radii. The information-carrying orthogonal mode light coupled into one channel is transmitted in a 25KM few-mode fiber.

At the receiving end, contrary to the working process of the transmitting end, the optical signal at the receiving end first passes through an optical filter, which can filter out the amplifier spontaneous emission noise (ASE) noise generated by the EDFA in the transmitting end, as well as the channel noise. Then, the received optical power is adjusted through an adjustable optical attenuator (VOA), and the photodetector is used to detect the received optical signal and convert it into an electrical signal. Finally, the three-dimensional APPM demodulation and bit error rate calculation are performed on the computer.

In order to illustrate that the method described in the patent has improved bit error performance, we list some eigenvalues of APPM, three-dimensional APPM (3D-APPM), 3D-CAP8, and 3D-CAP16 in Table 1. According to the formula of information entropy, the information entropy of 2×4 APPM and 3D APPM can be calculated to be 0.75 and 2.25, respectively. Therefore, the transmission capacity of 3D APPM with 3D multiplexing can be regarded as three times that of traditional APPM. In the comparison of 3D APPM with 3D-CAP8 and 3D-CAP16, the upsampling factor of 3D-CAP-16 is firstly set as 16, and on this basis, the upsampling factor of the other two modulation formats under the same transmission rate is calculated. , from the analysis of the results in Table 1, it can be concluded that the upsampling rate factor of the three-dimensional APPM is lower than the other two schemes, that is, the occupied bandwidth is smaller, which proves that the proposed scheme has improved spectrum utilization compared with the traditional scheme.

Table 1 Comparison of 3D APPM with 3D-CAP8 and 3D-CAP16

In order to further illustrate that the proposed scheme has good bit error performance, the simulation is carried out in a Gaussian white noise channel. The set sampling multiples are shown in Table 1. The obtained bit error performance simulation results are shown in Figure 6. When it is 10 ^-3 , the signal-to-noise ratios of 3D APPM, 3D-CAP8, and 3D-CAP16 are: 3.3dB, 4.13dB, and 6.71dB, respectively. Compared with 3D-CAP8 and 3D-CAP16, the 3D APPM achieves SNR gains of 0.83dB and 3.41dB, respectively. It shows that the proposed scheme improves the bit error performance of the system.

The above are only the preferred embodiments of the present invention. For those skilled in the art, without departing from the technical principle of the present invention, several improvements and modifications can also be made, and these improvements and modifications should also be regarded as The protection scope of the present invention.

Claims (6)

1. based on the orthogonal mode multiplexing transmission method of three-dimensional pulse amplitude position modulation, it is characterized in that: the original data of input completes coding mapping in the APPM mapping unit after the serial-parallel conversion unit carries out serial-parallel conversion, and the encoded signal passes through the After the sampling unit, the filter unit performs orthogonal filtering, and the orthogonally filtered signal is added by the adder unit to synthesize a three-dimensional APPM signal for orthogonal mode transmission; including the following steps: 1) The serial-parallel conversion unit converts the input original data into parallel transmission data; 2) The data transmitted in parallel in the step 1) obtains the signal mapped by the APPM through the APPM mapping unit, and then performs encoding and transmission; 3) Up-sampling the APPM-mapped signal described in step 2) by the up-sampling unit to realize the periodic extension of the signal on the spectrum, and obtain three APPM signals; in the up-sampling unit, perform a certain multiple of Sampling can recover the transmitted information at the receiving end, while reducing the number of taps required by the filter; 4) Filter the signal obtained in step 3) by the filter unit; multiply the APPM signal after the upsampling unit by three mutually orthogonal filters to maintain the orthogonality of the three APPM signals; 5) Synthesize the three APPM signals in step 4) into one through the adder unit to obtain a complete three-dimensional APPM signal, which is then transmitted in the orthogonal mode multiplexing system. 2. The orthogonal mode multiplexing transmission method based on three-dimensional pulse amplitude and position modulation according to claim 1, characterized in that: in step 1), the input original data is divided into three data after serial-parallel conversion stream for multi-dimensional multiplexing. 3. The quadrature mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation according to claim 2, characterized in that: in step 2), the three data streams generated by the serial-parallel change are respectively processed by the APPM mapping unit for 2 ×4APPM mapping. 4. The quadrature mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation according to claim 3, characterized in that: in the 2×4 APPM, each symbol has three bits, and one bit is used for amplitude matching , two bits are used for position matching; among them, i represents the amplitude bit, {0}, {1} correspond to two different amplitudes v ₁ , v ₂ , the probability of the occurrence of pulses with two different amplitudes is equal, which is 1 /2; j represents the position bit, and the combination of { y ₁ , y ₂ } is used to select one of the four time slots for energy signal filtering, and the process of pulse amplitude position modulation is completed through the selection and combination of i and j . 5. The quadrature mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation according to claim 1, characterized in that: in step 4), the filtering of the signal obtained in step 3) is performed by using a maximal polar The small optimization algorithm obtains three mutually orthogonal filter units, and the frequency response curve formula of the orthogonal filter is expressed as:

Among them, f _i is the impulse response of the i -th filter at the sending end, f ₁ is the impulse response of the first filter at the sending end, f ₂ is the impulse response of the second filter at the sending end, and f ₃ is the first filter at the sending end Three-way filter impulse response; F is the frequency amplitude characteristic of f _i , F ₁ is the frequency amplitude characteristic of filter f ₁ , F ₂ is the frequency amplitude characteristic of filter f ₂ , and F ₃ is the frequency of filter f ₃ Amplitude characteristics; H is the target bandpass frequency response; R(Z) is the polyphase decomposition of the receiver filter bank in the linear constraint, S(Z) is the polyphase decomposition of the transmitter filter bank, Γ is the permutation matrix, I is a unit matrix, Z - ⁿ represents n delay elements, and the matched filter of the response of the receiving end is calculated through this linear constraint _; using the optimization principle, make 1F1 _- H1 , 1F2 _- H1 , 1F3 The largest one of the three terms of -H1 tends to be the smallest, and finally, through iterative optimization, the part of the transmit filter F _i beyond the target bandpass frequency response tends to be the smallest. 6. The quadrature mode multiplexing transmission method based on three-dimensional pulse amplitude position modulation according to claim 1, characterized in that: in step 5), the three-way APPM signal in step 4) is converted by the adder unit Synthesis one way, specifically: at the transmitting end, according to the principle of orthogonalized mode field with the mode field correlation coefficient being 0, the continuous light generated by the laser source is controlled by the mode field after passing through the SLM, and the orthogonal mode light with different mode spot radii is output. , providing optical input for the MZM to achieve intensity modulation; the three-dimensional APPM on the electrical domain converts the digital signal into an analog signal waveform through a digital-to-analog converter, which is then used to drive the MZM; the light of each mode loaded with the three-dimensional APPM is transmitted through an erbium-doped fiber amplifier. After the light is amplified, it is combined by an orthogonal photonic coupler.

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